Commercial lamps which utilize incandescent, halogen, or high intensity discharge (HID) light sources have relatively high operating temperatures. As a consequence, heat egress is dominated by radiative and convective heat transfer pathways. Thermal management for incandescent, halogen, and HID light sources therefore typically amounts to providing adequate air space proximate the lamp for efficient radiative and convective heat transfer. Thus, it is usually not necessary to increase or modify the surface area of the lamp to enhance the radiative or convective heat transfer to achieve a desired operating temperature for these types of lamps.
As compared to incandescent lamps and halogen lamps, solid-state lighting technologies such as light-emitting diode (LED) devices are highly directional, and thus such devices typically emit light from only one side. But LED-based lamps are more energy efficient than incandescent or halogen lamps, for example, and typically have a longer operating life. In addition, LED-based lamps are durable, can operate under cold or hot temperatures, brighten quickly upon power-up, are ecologically friendly, and utilize low-voltage power supplies. Due to the many advantages associated with LED-based lamps, LED lamps have been produced to replace conventional Edison-base incandescent lamps and halogen light sources.
LED lamps typically operate at substantially lower temperatures for device performance and reliability reasons. For example, the junction temperature for a typical LED device can be below 200° C., and in some LED devices the junction temperatures are below 100° C. or even lower. However, at such low operating temperatures, the radiative heat transfer pathway to the ambient air is weak, so that convective and conductive heat transfer to the ambient air typically dominates. Thus, LED light sources typically utilize a heat sink connected to the LED light source to enhance the convective and radiative heat transfer from the outside surface area of the lamp or luminaire.
A heat sink is a component that provides a large surface area to radiate and/or convect heat away from one or more LED devices. The heat sink is typically a relatively massive metal element that has a large engineered surface area, for example by including fins as heat dissipating structures that radiate outwardly from a surface. A massive heat sink efficiently conducts heat from the LED devices to the fins, and the large surface area of the fins provides efficient heat egress by radiation and convection. In the case of high power LED-based lamps, active cooling elements have been used to enhance heat removal. Examples of active cooling elements include fans, synthetic jets, heat pipes, thermo-electric coolers, and/or pumped coolant fluid.
Another design challenge associated with solid-state lamps is that, unlike an incandescent filament, an LED chip or other solid-state lighting device typically cannot be operated efficiently using standard 110V or 220V alternating current (A.C.) power. Thus, on-board electronic components are needed to convert the A.C. input to direct current (D.C.) power having a lower voltage for driving the LED chips. Such electronic components are typically included within the lamp base (below the heat sink component), in contrast to the simple Edison base used in conventional incandescent lamps or halogen lamps.
Accordingly, LED replacement lamps (to replace, for example, conventional incandescent A19-type light bulbs and/or parabolic aluminized reflector (PAR) type lamps) must balance thermal management principals, such as lamp size constraints, lamp power balance and lamp thermal impedance, and must also consider aesthetics (the shape, size and color characteristics of the LED lamp). In particular, LED replacement lamps have been designed to match “legacy” lamps (such as the A19 soft white light bulb and/or the PAR38 type lamp) in size and shape, in unlit appearance, in lit appearance (i.e., no visible LED dots), in beam distribution, and in color quality. In addition, LED replacement lamps are typically designed to meet “Energy Star” requirements that include having a uniform light intensity plus or minus twenty percent (+/−20%) through a range of vertical angles from zero degrees (0°) to one-hundred and thirty-five degrees (135°), even though LEDs radiate primarily in the forward direction.
As mentioned above, a challenging aspect of LED lamp design for a replacement LED lamp that will be used in an Edison socket concerns managing the waste heat from the LEDs due to the regulated size constraints of the lamp and the insufficient thermal conductance of the Edison base. Thus, a need exists for methods and apparatus to efficiently and inexpensively manage the waste heat from the LEDs of an LED replacement lamp.